This invention relates to bicomponent nonwoven webs containing splittable thermoplastic filaments and a third component selected from fibers, particles and combinations thereof. The splitting of bicomponent filaments into smaller filaments helps to contain the third component, and may add softness to the composite product. Also, better capillary may result from the increased filament surface area.
Bicomponent nonwoven filaments are known in the art generally as thermoplastic filaments which employ at least two different polymers combined together in a heterogeneous fashion. Instead of being homogeneously blended, two polymers may, for instance, be combined in a side-by-side configuration, so that a first side of a filament is composed of a first polymer xe2x80x9cAxe2x80x9d and a second side of the filament is composed of a second polymer xe2x80x9cB.xe2x80x9d Alternatively, the polymers may be combined in a sheath-core configuration, so that an outer sheath layer of a filament is composed of a first polymer xe2x80x9cA,xe2x80x9d and the inner core is composed of a second polymer xe2x80x9cB.xe2x80x9d Alternatively, the polymers may be combined in an islands-in-the-sea configuration in which one or more islands of a first polymer xe2x80x9cAxe2x80x9d appear in a sea of a second polymer xe2x80x9cB.xe2x80x9d Other heterogeneous configurations are also possible.
Splittable nonwoven bicomponent filaments are disclosed in U.S. Pat. No. 5,759,926, issued to Pike et al. These filaments contain at least two incompatible polymers arranged in distinct segments across the cross-section of each filament. The incompatible segments are continuous along the length of each filament. The individual segments of each filament split apart from each other when the filament is contacted with a hot aqueous fibrillation-inducing medium, resulting in finer individual filaments formed from the segments. Other techniques for splitting bicomponent filaments include mechanical agitation and spontaneous splitting caused by differential shrinkage of the components.
Bicomponent filaments have been disclosed in combination with carbon particles, zeolites, ion exchange resins, carbon fibers, stabilizing fibers, and/or gas absorbing fibers for use in specialized filters. U.S. Pat. No. 5,670,044, issued to Ogata et al., discloses the use of bicomponent meltblown filaments in these combinations, for use in cylindrical filters. In that case, the bicomponent filaments contain high and low melting polymers. The filaments of the filter are stacked and bonded together by melting only the lower melting component. However, Ogata et al. does not suggest splitting the bicomponent filaments.
Pulp fibers have been employed in certain absorbent applications, to enhance the absorbency. U.S. Pat. No. 4,530,353, issued to Lauritzen, discloses pulp fibers in combination with staple length bicomponent fibers used in the manufacture of absorbent bandages. In that case, the fibers also contain high and low melting polymers. The staple length fibers are bonded together by melting only the lower melting component. Again, there is no suggestion to split the bicomponent filaments.
In the field of absorbent articles, and other fields where thermoplastic nonwoven webs are combined with a third component selected from other fibers and/or particles, there is a need or desire for techniques which better contain the third component within the thermoplastic nonwoven filaments. There is also a need or desire for techniques which increase the maximum amount of the third component that can be ensnared, entangled, or otherwise contained within the matrix of thermoplastic nonwoven filaments.
The present invention is directed to an improved nonwoven composite wherein thermoplastic nonwoven filaments are utilized as a matrix for ensnaring, containing and restraining a component selected from other fibers and/or particles. The nonwoven composite provides improved containment of the other fibers and/or particles, and effectively contains higher levels of the other fibers and/or particles within a thermoplastic nonwoven filament matrix. The improved performance is accomplished using splittable thermoplastic bicomponent filaments, whose first and second polymers split apart into a larger number of finer filaments. The resulting finer filaments, in the increased number, provide better containment of the third component selected from other fibers and/or particles.
The present invention is also directed to an absorbent article, including a personal care absorbent article, which utilizes the improved nonwoven web composite of the invention.
The splittable bicomponent filaments contain at least first and second mutually incompatible thermoplastic polymer components, arranged in distinct segments across the width of the filament. Each polymer component is preferably continuous along the length of each splittable filament. Preferably, the splitting of the segments is controllable, so that the third component (other pulp or particles) can be combined relatively easily with the bicomponent filaments before they are split. Thereafter, the bicomponent filaments are responsive to a control mechanism which induces splitting of the filaments into finer filaments corresponding to each segment, to more firmly entrap and ensnare the third component within the matrix of thermoplastic filaments. Preferably, the splittable bicomponent filaments, and the thermoplastic segment components thereof, are substantially continuous in length.
With the foregoing in mind, it is a feature and advantage of the invention to provide an improved nonwoven web composite which exhibits improved containment of a third component selected from fibers and/or particles, within a matrix of thermoplastic nonwoven filaments.
It is also a feature and advantage of the invention to provide a nonwoven web composite having a latent controlled containment mechanism, which improves the ensnaring and entrapment of the third component after the third component enters the thermoplastic filament matrix.
It is also a feature and advantage of the invention to provide an absorbent article made using the improved nonwoven web composite.
The term xe2x80x9cnonwoven fabric or webxe2x80x9d means a web having a structure of individual fibers or threads which are interlaid, but not in a regular or identifiable manner as in a knitted fabric. Nonwoven fabrics or webs have been formed from many processes such as, for example, meltblowing processes, spunbonding processes, air laying processes, and bonded carded web processes. The basis weight of nonwoven fabrics is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm) and the fiber diameters useful are usually expressed in microns. (Note that to convert from osy to gsm, multiply osy by 33.91.)
The term xe2x80x9cmicrofibersxe2x80x9d means small diameter fibers having an average diameter not greater than about 75 microns, for example, having an average diameter of from about 1 micron to about 50 microns, or more particularly, microfibers may have an average diameter of from about 1 micron to about 30 microns. Another frequently used expression of fiber diameter is denier, which is defined as grams per 9000 meters of a fiber. For a fiber having circular cross-section, denier may be calculated as fiber diameter in microns squared, multiplied by the density in grams/cc, multiplied by 0.00707. A lower denier indicates a finer fiber and a higher denier indicates a thicker or heavier fiber. For example, the diameter of a polypropylene fiber given as 15 microns may be converted to denier by squaring, multiplying the result by 0.89 g/cc and multiplying by 0.00707. Thus, a 15 micron polypropylene fiber has a denier of about 1.42 (152xc3x970.89xc3x970.00707=1.415). Outside the United States the unit of measurement is more commonly the xe2x80x9ctex,xe2x80x9d which is defined as the grams per kilometer of fiber. Tex may be calculated as denier/9. The foregoing range refers to diameters existing before any splitting. The splitting of bicomponent microfibers would result in correspondingly smaller diameters.
The term xe2x80x9cspunbonded fibersxe2x80x9d refers to small diameter fibers which are formed by extruding molten thermoplastic material as filaments from a plurality of fine capillaries of a spinnerette having a circular or other configuration, with the diameter of the extruded filaments then being rapidly reduced as by, for example, in U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to Hartman, U.S. Pat. No. 3,502,538 to Petersen, and U.S. Pat. No. 3,542,615 to Dobo et al., each of which is incorporated herein in its entirety by reference. Spunbond fibers are quenched and generally not tacky when they are deposited onto a collecting surface. Spunbond fibers are generally continuous and often have average diameters larger than about 7 microns, more particularly, between about 10 and 30 microns. Again, the splitting of bicomponent spunbonded fibers would result in correspondingly smaller diameters.
The term xe2x80x9cmeltblown fibersxe2x80x9d means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity heated gas (e.g., air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Such a process is disclosed for example, in U.S. Pat. No. 3,849,241 to Butin. Meltblown fibers are microfibers which may be continuous or discontinuous, are generally smaller than 10 microns in diameter, and are generally self bonding when deposited onto a collecting surface. Meltblown fibers used in the present invention are preferably substantially continuous in length. Again, the splitting of bicomponent meltblown fibers would produce smaller diameter fibers.
The term xe2x80x9csubstantially continuous filaments or fibersxe2x80x9d refers to filaments or fibers prepared by extrusion from a spinnerette, including without limitation spunbonded and meltblown fibers, which are not cut from their original length prior to being formed into a nonwoven web or fabric. Substantially continuous filaments or fibers may have average lengths ranging from greater than about 15 cm to more than one meter, and up to the length of the web or fabric being formed. The definition ofxe2x80x9csubstantially continuous filaments or fibersxe2x80x9d includes those which are not cut prior to being formed into a nonwoven web or fabric, but which are later cut when the nonwoven web or fabric is cut.
The term xe2x80x9cstaple fibersxe2x80x9d means fibers which are natural or cut from a manufactured filament prior to forming into a web, and which have an average length ranging from about 0.1-15 cm, more commonly about 0.2-7 cm.
The term xe2x80x9cpersonal care absorbent articlexe2x80x9d includes diapers, training pants, swim wear, absorbent underpants, baby wipes, adult incontinence products, and feminine hygiene products.
The term xe2x80x9cbicomponent filaments or fibersxe2x80x9d refers to fibers which have been formed from at least two polymers extruded from separate extruders but spun together to form one fiber. The polymers are arranged in substantially constantly positioned distinct zones across the cross-section of the bicomponent fibers and extend continuously along the length of the bicomponent fibers. The configuration of such a bicomponent fiber may be, for example, a sheath/core arrangement wherein one polymer is surrounded by another or may be a side-by-side arrangement or an xe2x80x9cislands-in-the-seaxe2x80x9d arrangement. Bicomponent fibers are taught in U.S. Pat. No. 5,108,820 to Kaneko et al., U.S. Pat. No. 5,336,552 to Strack et al., and U.S. Pat. No. 5,382,400 to Pike et al., each of which is incorporated herein in its entirety by reference. For two component fibers, the polymers may be present in ratios of 75/25, 50/50, 25/75 or any other desired ratios. Conventional additives, such as pigments and surfactants, may be incorporated into one or both polymer streams, or applied to the filament surfaces.
The term xe2x80x9csplittable bicomponent filamentsxe2x80x9d refers to bicomponent filaments, as described above, which split lengthwise into finer filaments of the individual thermoplastic polymer segments when subjected to a stimulus. The term xe2x80x9ccontrolled splittingxe2x80x9d refers to subjecting these bicomponent filaments to a controlled stimulus or process which effects the lengthwise splitting at a selected time and place.
The term xe2x80x9cpulp fibersxe2x80x9d refers to fibers from natural sources such as woody and non-woody plants. Woody plants include, for example, deciduous and coniferous trees. Non-woody plants include, for instance, cotton, flax, esparto grass, milkweed, straw, jute hemp, and bagasse.
The term xe2x80x9caverage fiber lengthxe2x80x9d refers to a weighted average length of fibers determined using a Kajaani fiber analyzer Model No. FS-100 available from Kajaani Oy Electronics in Kajaani, Finland. Under the test procedure, a fiber sample is treated with a macerating liquid to ensure that no fiber bundles or shives are present. Each fiber sample is dispersed in hot water and diluted to about a 0.001% concentration. Individual test samples are drawn in approximately 50 to 500 ml portions from the dilute solution and tested using the standard Kajaani fiber analysis procedure. The weighted average fiber lengths may be expressed by the following equation:       ∑                  X        i             greater than       0        k    ⁢      xe2x80x83    ⁢            (                        X          i                *                  n          i                    )        ⁢          /        ⁢    n  
where k=maximum fiber length,
Xi=individual fiber length,
ni=number of fibers having length Xi 
and n=total number of fibers measured.
The term xe2x80x9csuperabsorbentxe2x80x9d or xe2x80x9csuperabsorbent materialxe2x80x9d refers to a water-swellable, water-insoluble organic or inorganic material capable, under the most favorable conditions, of absorbing at least about 20 times its weight and, more desirably, at least about 30 times its weight in an aqueous solution containing 0.9 weight percent sodium chloride.
The term xe2x80x9cpolymerxe2x80x9d includes, but is not limited to, homopolymers, copolymers, such as for example, block, graft, random and alternating copolymers, terpolymers, etc. and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term xe2x80x9cpolymerxe2x80x9d shall include all possible geometrical configurations of the material. These configurations include, but are not limited to isotactic, syndiotactic and atactic symmetries.
The term xe2x80x9cincompatible polymersxe2x80x9d indicates polymers that do not form a miscible blend, i.e., immiscible, when melt blended. As a desirable embodiment of the present invention, differences in the polymer solubility parameter (xcex4) may be used to select suitably incompatible polymers. The polymer solubility parameters (xcex4) of different polymers are well known in the art. A discussion of the solubility parameter is, for example, disclosed in Polymer: Chemistry and Physics of Modern Materials, pages 142-145, by J. M. G. Cowie, International Textbook Co., Ltd., 1973. Desirably, the adjacently disposed polymer components of the present conjugate fiber have a difference in the solubility parameter of at least about 0.5 (cal/cm3)1/2, more desirably at least about 1 (cal/cm3)1/2, most desirably at least about 2 (cal/cm3)1/2. The upper limit of the solubility parameter difference is not critical for the present invention as long as 1) the filaments do not split prematurely so as to interfere with spinning, and 2) there is adequate control over the splitting.
The term xe2x80x9cthrough-air bondingxe2x80x9d or xe2x80x9cTABxe2x80x9d means a process of bonding a nonwoven, for example, a bicomponent fiber web in which air which is sufficiently hot to melt one of the polymers of which the fibers of the web are made is forced through the web. The air velocity is often between 100 and 500 feet per minute and the dwell time may be as long as 6 seconds. The melting and resolidification of the polymer provides the bonding. Through-air bonding has restricted variability and is generally regarded as a second step bonding process. Since TAB requires the melting of at least one component to accomplish bonding, it is restricted to webs with two components such as bicomponent fiber webs or webs containing an adhesive fiber or powder.
The term xe2x80x9cthermal point bondingxe2x80x9d involves passing a fabric or web of fibers to be bonded between a heated calender roll and an anvil roll. The calender roll is usually, though not always, patterned in some way so that the entire fabric is not bonded across its entire surface. As a result, various patterns for calender rolls have been developed for functional as well as aesthetic reasons. One example of a pattern has points and is the Hansen Pennings or xe2x80x9cHandPxe2x80x9d pattern with about a 30% bond area with about 200 bonds/square inch as taught in U.S. Pat. No. 3,855,046 to Hansen and Pennings. The HandP pattern has square point or pin bonding areas wherein each pin has a side dimension of 0.038 inches (0.965 mm), a spacing of 0.070 inches (1.778 mm) between pins, and a depth of bonding of 0.023 inches (0.584 mm). The resulting pattern has a bonded area of about 29.5%. Another typical point bonding pattern is the expanded Hansen and Pennings or xe2x80x9cEHPxe2x80x9d bond pattern which produces a 15% bond area with a square pin having a side dimension of 0.037 inches (0.94 mm), a pin spacing of 0.097 inches (2.464 mm) and a depth of 0.039 inches (0.991 mm). Another typical point bonding pattern designated xe2x80x9c714xe2x80x9d has square pin bonding areas wherein each pin has a side dimension of 0.023 inches, a spacing of 0.062 inches (1.575 mm) between pins, and a depth of bonding of 0.033 inches (0.838 mm). The resulting pattern has a bonded area of about 15%. Yet another common pattern is the C-Star pattern which has a bond area of about 16.9%. The C-Star pattern has a cross-directional bar or xe2x80x9ccorduroyxe2x80x9d design interrupted by shooting stars. Other common patterns include a diamond pattern with repeating and slightly offset diamonds and a wire weave pattern looking as the name suggests, e.g., like a window screen. Typically, the percent bonding area varies from around 10% to around 30% of the area of the fabric laminate web. As is well known in the art, the spot bonding holds the laminate layers together as well as imparts integrity to each individual layer by bonding filaments and/or fibers within each layer.